Delayed degradation of chlorophylls and photosynthetic proteins in Arabidopsis autophagy mutants during stress-induced leaf yellowing

Under mild abiotic-stress conditions, Arabidopsis atg mutants showed a functional stay-green phenotype which is probably caused by the lack of chloroplastic autophagy and the retrograde regulation of senescence-associated gene expressio

Rice Basic Helix-Loop-Helix 079 (OsbHLH079) Delays Leaf Senescence by Attenuating ABA Signaling

Leaf senescence represents the final phase of leaf development and is characterized by a highly organized degenerative process involving the active translocation of nutrients from senescing leaves to growing tissues or storage organs. To date, a large number of senescence-associated transcription factors (sen-TFs) have been identified that regulate the initiation and progression of leaf senescence. Many of these TFs, including NAC (NAM/ATAF1/2/CUC2), WRKY, and MYB TFs, have been implicated in modulating the expression of downstream senescence-associated genes (SAGs) and chlorophyll degradation genes (CDGs) under the control of phytohormones. However, the involvement of basic helix-loop-helix (bHLH) TFs in leaf senescence has been less investigated. Here, we show that OsbHLH079 delays both natural senescence and dark-induced senescence: Overexpression of OsbHLH079 led to a stay-green phenotype, whereas osbhlh079 knockout mutation displayed accelerated leaf senescence. Similar to other sen-TFs, OsbHLH079 showed a gradual escalation in expression as leaves underwent senescence. During this process, the mRNA levels of SAGs and CDGs remained relatively low in OsbHLH079 overexpressors, but increased sharply in osbhlh079 mutants, suggesting that OsbHLH079 negatively regulates the transcription of SAGs and CDGs under senescence conditions. Additionally, we found that OsbHLH079 delays ABA-induced senescence. Subsequent RT-qPCR and dual-luciferase reporter assays revealed that OsbHLH079 downregulates the expression of ABA signaling genes, such as OsABF2, OsABF4, OsABI5, and OsNAP. Taken together, these results demonstrate that OsbHLH079 functions in delaying leaf yellowing by attenuating the ABA responses.This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (NRF-2022R1A2C1091553

The Rice SPOTTED LEAF4 (SPL4) Encodes a Plant Spastin That Inhibits ROS Accumulation in Leaf Development and Functions in Leaf Senescence

Lesion mimic mutants (LMMs) are usually controlled by single recessive mutations that cause the formation of necrotic lesions without pathogen invasion. These genetic defects are useful to reveal the regulatory mechanisms of defense-related programmed cell death in plants. Molecular evidence has been suggested that some of LMMs are closely associated with the regulation of leaf senescence in rice (Oryza sativa). Here, we characterized the mutation underlying spotted leaf4 (spl4), which results in lesion formation and also affects leaf senescence in rice. Map-based cloning revealed that the gamma ray-induced spl4-1 mutant has a single base substitution in the splicing site of the SPL4 locus, resulting in a 13-bp deletion within the encoded microtubule-interacting-and-transport (MIT) spastin protein containing an AAA-type ATPase domain. The T-DNA insertion spl4-2 mutant exhibited spontaneous lesions similar to those of the spl4-1 mutant, confirming that SPL4 is responsible for the LMM phenotype. In addition, both spl4 mutants exhibited delayed leaf yellowing during dark-induced or natural senescence. Western blot analysis of spl4 mutant leaves suggested possible roles for SPL4 in the degradation of photosynthetic proteins. Punctate signals of SPL4-fused fluorescent proteins were detected in the cytoplasm, similar to the cellular localization of animal spastin. Based on these findings, we propose that SPL4 is a plant spastin that is involved in multiple aspects of leaf development, including senescence

Regulation of anthocyanin synthesis and embryo quiescence by Viviparous-1 and abscistic acid during maize kernel development

Vita.Abscisic acid (ABA) is required as a co-regulatory factor for all of the regulatory functions associated with Viviparous-1 (Vp1) during maize kernel development. The exception has been anthocyanin synthesis, because carotenoid-deficient viviparous mutants have reduced endogenous ABA but still accumulate anthocyanin pigments. However, if full color kernel blocks are cultured on fluridone medium to reduce endogenous ABA to near zero levels, anthocyanin synthesis is repressed. Addition of exogenous ABA to fluridone medium induces anthocyanin synthesis. Vp1 is expressed in the presence or absence of ABA, but C1 is expressed only when ABA is present. The content of C1 transcripts is increased by adding exogenous ABA into standard medium. When all dominant genes for anthocyanin expression in aleurone tissue are present, the timing and intensity of anthocyanin expression depend on ABA concentration. Both maternal and exogenous ABA are transported into developing maize kernels, and the source of ABA is irrelevant. Genes coding for maize lipase (LIP) and malate synthase (MS) enzymes involved in lipolysis and glyoxylate cycle during germination were cloned to elucidate the Vp1 and ABA regulatory role for the induction of embryo quiescence. The MS and LIP genes are expressed in ABA-insensitive (vp1) and ABA-deficient (vp7, vp10) mutants but not in wild-type embryos at 26 days after pollination (DAP). It appears that Vp1 and ABA regulation is involved in the repression of germination genes at the transcriptional level. This suggests that two major regulatory systems exist for preventing vivipary. The one set of germination genes is down-regulated by ABA alone and the other is by Vp1 and ABA to induce embryo quiescence during maize kernel development. The Vp1 transcription activator regulates the target genes in specific tissue types and then the level of expression is controlled by the concentration of ABA in developing maize kernels

Regulation of anthocyanin synthesis and embryo quiescence by Viviparous-1 and abscistic acid during maize kernel development

Vita.Abscisic acid (ABA) is required as a co-regulatory factor for all of the regulatory functions associated with Viviparous-1 (Vp1) during maize kernel development. The exception has been anthocyanin synthesis, because carotenoid-deficient viviparous mutants have reduced endogenous ABA but still accumulate anthocyanin pigments. However, if full color kernel blocks are cultured on fluridone medium to reduce endogenous ABA to near zero levels, anthocyanin synthesis is repressed. Addition of exogenous ABA to fluridone medium induces anthocyanin synthesis. Vp1 is expressed in the presence or absence of ABA, but C1 is expressed only when ABA is present. The content of C1 transcripts is increased by adding exogenous ABA into standard medium. When all dominant genes for anthocyanin expression in aleurone tissue are present, the timing and intensity of anthocyanin expression depend on ABA concentration. Both maternal and exogenous ABA are transported into developing maize kernels, and the source of ABA is irrelevant. Genes coding for maize lipase (LIP) and malate synthase (MS) enzymes involved in lipolysis and glyoxylate cycle during germination were cloned to elucidate the Vp1 and ABA regulatory role for the induction of embryo quiescence. The MS and LIP genes are expressed in ABA-insensitive (vp1) and ABA-deficient (vp7, vp10) mutants but not in wild-type embryos at 26 days after pollination (DAP). It appears that Vp1 and ABA regulation is involved in the repression of germination genes at the transcriptional level. This suggests that two major regulatory systems exist for preventing vivipary. The one set of germination genes is down-regulated by ABA alone and the other is by Vp1 and ABA to induce embryo quiescence during maize kernel development. The Vp1 transcription activator regulates the target genes in specific tissue types and then the level of expression is controlled by the concentration of ABA in developing maize kernels

Quantitative Trait Locus Mapping and Candidate Gene Analysis for Functional Stay-Green Trait in Rice

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.Functional stay-green (FSG) delays leaf yellowing, maintaining photosynthetic competence, whereas nonfunctional stay-green (NFSG) retains only leaf greenness without sustaining photosynthetic activity. Retention of chlorophylls and photosynthetic capacity is important for increasing crop yield. We determined the main-effect quantitative trait loci (QTLs) for FSG traits in the japonica rice SNU-SG1 and isolated candidate genes. To identify QTLs influencing FSG, we analyzed eight traits: (1) 1 day after heading-degree of chlorophyll content of flag leaf, (2) 1 day after heading-degree of chlorophyll content of second leaf, (3) 1 day after heading-degree of chlorophyll content of flag and second leaves, (4) 50 day after heading-degree of chlorophyll content of flag leaf, (5) 50 day after heading-degree of chlorophyll content of second leaf, (6) 50 day after heading-degree of chlorophyll content of flag and second leaves, (7) relative decline degree of chlorophyll content of flag and second leaves, and (8) flowering time. We carried out QTL analysis with F7 RIL from a cross of japonica rice SNU-SG1 and indica rice Milyang23 (M23). Using 131 molecular markers, we identified 18 QTLs for the eight traits with a threshold LOD value > 2.8. Sequence analysis identified 16 candidate genes for 10 main-effect QTLs. Of these, we have chosen seven strong candidate genes for the 10 main-effect QTLs. These genetic resources will be useful for breeding high-yielding rice cultivars.OAIID:oai:osos.snu.ac.kr:snu2015-01/102/0000003606/7ADJUST_YN:YEMP_ID:A002118DEPT_CD:517CITE_RATE:0FILENAME:2015-7 fsg (plant breed biotechnol)-임정현.pdfDEPT_NM:식물생산과학부SCOPUS_YN:NCONFIRM:

Gibberellic Acid: A Key Phytohormone for Spikelet Fertility in Rice Grain Production

The phytohormone gibberellic acid (GA) has essential signaling functions in multiple processes during plant development. In the “Green Revolution”, breeders developed high-yield rice cultivars that exhibited both semi-dwarfism and altered GA responses, thus improving grain production. Most studies of GA have concentrated on germination and cell elongation, but GA also has a pivotal role in floral organ development, particularly in stamen/anther formation. In rice, GA signaling plays an important role in spikelet fertility; however, the molecular genetic and biochemical mechanisms of GA in male fertility remain largely unknown. Here, we review recent progress in understanding the network of GA signaling and its connection with spikelet fertility, which is tightly associated with grain productivity in cereal crops

Salt treatments and induction of senescence

High salinity, one of the most severe abiotic stresses encountered by land plants, often results from water deficit and also induces whole-plant senescence. Thus, salt treatment provides a useful technique for stress-mediated induction of senescence in plants. In this chapter, we describe the procedures to induce senescence in Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa), using NaCl or KCl. Furthermore, we present experimental approaches to measure salt stress-induced leaf senescence.© Springer Science+Business Media, LLC 2008.N